1. Field of the Invention
This invention relates to a magnetic tape cartridge and more particularly to a magnetic tape cartridge holding therein a single reel on which a magnetic tape is wound and including a leader block holding an end of the tape, which leader block is attachable to and detachable from a tape outlet.
2. Background
Conventionally, magnetic tape cartridges used as a recording medium for a computer or the like include a magnetic tape cartridge in which a magnetic tape T is would on a single reel 14. The reel 14 is rotatably contained in a cartridge 101 composed of an upper case 13 and a lower case 1, as shown in FIG. 1. As illustrated in FIG. 2, when the magnetic tape cartridge is not in use, a leader block 3, attached to the leading tape end, is detachably engaged in a tape outlet 2 formed in a corner of the cartridge 101 and retained there to prevent the reel 14 from accidental angular movement, with the magnetic tape T completely wound therearound.
The reel 14 has a hub 17 at a center portion thereof and the hub 17 has an annular wall which, upon assemblage of the cartridge, is disposed in surrounding relation to a brake button 15 mounted on the lower case 1 and held in an urged condition by a coil spring 16. Braking teeth 25 of a serrated shape are formed on an outer peripheral portion of the lower face of the brake button 15 and circumferentially spaced from one another. The braking teeth are meshingly engaged with braking teeth (not shown) formed on the reel 14 and disposed within the hub 17 so as to prevent the accidental angular movement of the reel 14. The cartridge 101, when in use, is loaded into the device such as a computer, and for example, a rotatable shaft of a motor is introduced into the cartridge 101 and is brought into engagement with the brake button 15 to urge the button inwardly of the cartridge 101 against the bias of the coil spring 16. As a result, the locking of the reel 14 is released so that the reel 14 can be rotated.
Thereafter, a withdrawing pin (not shown) provided in the above-mentioned device is suitably engaged with the leader block 3 disposed in the tape outlet 2, so that the leader block 3 is withdrawn exteriorly of the cartridge 101 and is connected to a take-up reel in the device in a unitary manner to enable the travel of the tape.
As shown in FIGS. 2 and 3 the leader block 3 comprises a resin block having a generally rectangular horizontal cross-section. The leader block 3 has at a front end thereof a withdrawal engaging portion 7 having a generally cylindrical stepped inner peripheral surface extending in the direction of the width of the case. The withdrawing pin provided in the device such as a computer is engageable in the withdrawal engaging portion 7. A rear end face of the leader block 3, opposing the withdrawal engaging portion 7, is formed into a curved surface 10 which has the same curvature in a horizontal direction as the outer peripheral surface of the take-up reel in the device, so as to form part of the outer peripheral surface of the take-up reel when the leader block 3 is connected to the take-up reel. Also, the leader block 3 has a recess 8 having a generally cylindrical peripheral surface formed in a side face of the leader block 3 directed inwardly in the case. The recess 8 serves to clamp the leading end of the magnetic tape T in cooperation with a clamp member 6.
Partition walls 9 for suitably holding the leader block 3 in position are provided at the tape outlet 2 and are formed on the inner surfaces of the upper and lower cases 13 and 1, respectively. The partition walls 9 correspond in shape to the side face of the leader block 3 directed inwardly of the case and the curved surface 10 so as to hold the leader block 3 against movement in a horizontal direction. The portion of a side wall 5 of the upper case 13 disposed forwardly of a front end portion 4 of the leader block 3 and in opposed relation thereto is adapted to be abutted against the front end portion 4 when the leader block 3 is attached and detached. The side wall 5 can be suitably deformed so that the leader block 3 can be attached and detached.
Therefore, in accordance with the degree of abutment of the front end portion 4 against the side wall 5 at the time of attaching and detaching the leader block 3, the force required for attaching the leader block 3 as well as the force for withdrawing is determined.
Referring to FIG. 4, the withdrawing pin 19 is suitably fitted in the withdrawal engaging portion 7 so as to effect the attachment and detachment of the leader block 3. More specifically, the leader block 3 has a stepped recess 20 of a generally cylindrical shape formed adjacent to a lower end of a withdrawal engaging portion 7 and having a diameter greater than a groove width of the withdrawal engaging portion 7. The withdrawing pin 19 has a shoulder portion 21 formed at a front end of its body 22 so as to be correspondingly fitted in the stepped recess 20. When the magnetic tape cartridge is loaded into the device such as a computer, the pin body 22 is first received in the withdrawal engaging portion 7 from the front end of the leader block 3, and then the cartridge is moved downwardly, so that the shoulder portion 21 is fitted in the stepped recess 20 of the leader block 3. Then, when the withdrawing pin 19 is moved in a horizontal direction, the leader block 3 is also withdrawn exteriorly of the cartridge in such a manner that the leader block is kept integral with the shoulder portion 21.
When the withdrawing pin 19 is horizontally moved exteriorly of the case in a direction indicated by an arrow A in FIG. 2, the leader block 3 is rotatably moved horizontally about a fulcrum defined by a point B of contact between the curved surface 10 and a curved portion 12 of the partition wall 9 disposed in opposed relation thereto. Thus, the front end portion 4 resiliently deforms the side wall 5 and is withdrawn exteriorly of the cartridge, with its front end first moved out of the cartridge. When the leader block 3 is to be attached to the tape outlet 2, the leader block 3 is inserted into the tape outlet 2 by the withdrawing pin 19, with its rear end first introduced. Upon engagement of the curved surface 10 with the curved portion 12 of the partition wall 9, the leader block 3 is rotatably moved horizontally about the contact point B in a direction reverse to the direction of movement at the time of the withdrawing operation. As a result, the front end portion 4 resiliently deforms the side wall 5, so that the leader block 3 is attached to the tape outlet 2.
Each time the leader block 3 is attached to and detached from the tape outlet 2, the withdrawing pin 19 is subjected to a bending force resulting from the attaching force or the withdrawing force for resiliently deforming the side wall 5 to attach or detach the leader block 3 with respect to the tape outlet 2. Thus, the withdrawing pin is repeatedly subjected to a bending force. Therefore, in order to prevent the deformation of the withdrawing pin, it is necessary that irregularities in the withdrawing force and attaching force, as well as these forces per se, be small.
However, the contact point B serving as the fulcrum for the horizontal rotational movement of the leader block 3 is disposed, with respect to the cartridge, outwardly of an extension of a straight line (which coincides with the center line X--X of the leader block 3) interconnecting a point of action (the portion where the front end portion 4 is abutted against the side wall 5) and a point of force (the engaging portion of the withdrawal engaging portion 7 on which the force of horizontal movement of the withdrawing pin acts).
When the leader block 3 is rotatably moved horizontally by the withdrawing pin about the contact point B so as to attach or detach the leader block with respect to the tape outlet 2, the attaching force acting on the withdrawing pin when the front end portion 4 resiliently deforms the side wall 5 to be received in the tape outlet 2 is greater than the withdrawing force acting on the withdrawing pin when the front end portion 4 resiliently deforms the side wall 5 to be withdrawn from the tape outlet 2, due to the relationship of dynamical positions of the point of action, the point of force and the fulcrum. Therefore, it has been difficult to stabilize the forces for attaching and detaching the leader block 3.
Furthermore, the case 1 as well as the leader block 3 must be made of a material which meets the flame retardant requirements (UL94V-2) to protect data in case of emergency, and for this reason, mainly, a polycarbonate resin is used. However, molded products of the flame retardant plastic resin such as a polycarbonate resin are subjected to large irregularities in dimensions In addition, such a resin has a high coefficient of friction although its wear resistance is high. Therefore, it has been difficult to stabilize the attaching and detaching forces for the leader block 3.
In addition, the flame retardant plastic resin, such as a polycarbonate resin, has a low mold shrinkage factor and a high coefficient of friction, and therefore as seen from the upper cartridge 3 in FIG. 5, the side wall 5 has a relatively large release inclination of .theta. so that the molded upper cartridge can easily be released from the mold, when molding the upper and lower cartridges.
Therefore, when the leader block 3 is attached and detached, the surface of contact of the front end portion 4 and side wall 5 is not uniform, rather the front end portion 4 and the side wall 5 are partially abutting each other proximate the side wall 5.
Furthermore, the position where the withdrawing pin 19 acts on the stepped recess 20 of the leader block 3 to apply the attaching and detaching force thereto is spaced from the position where the front end portion 4 of the leader block 3 acts on the side wall 5 to apply the abutting force thereto to suitably deform the same, and the directions of of these forces are inconsistent with each other. Therefore, each time the leader block is attached or detached, a twisting force is in some cases exerted on the withdrawing pin, so that the effective attaching and detaching force is increased, and in an extreme case, the withdrawing pin has been deformed.